//30.串联所有单词的子串（滑动窗口）
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Solution {
    public List<Integer> findSubstring(String s, String[] words) {
        List<Integer> ret = new ArrayList<>();

        Map<String,Integer> hash1 = new HashMap<>();//保存words中所有单词的频次
        for(String str : words){
            hash1.put(str,hash1.getOrDefault(str,0)+1);
        }

        int len = words[0].length();//words中每个字符串的长度
        int m = words.length;//words中有多少个单词数
        
        //滑动窗口执行次数
        for(int i = 0;i < len;i++){
            Map<String,Integer> hash2 = new HashMap<>();//保存窗口内所有单词的频次
            int count = 0;
            for(int left = i,right = i;right + len <= s.length();right += len){
                //进窗口+维护count
                String in = s.substring(right,right + len);
                hash2.put(in,hash2.getOrDefault(in,0) + 1);
                if(hash2.get(in) <= hash1.getOrDefault(in,0)){
                    count++;
                }
                //判断
                if(right - left +1 >len * m){
                    //出窗口+维护count
                    String out = s.substring(left,left + len);
                    if(hash2.get(out) <= hash1.getOrDefault(out,0)){
                        count--;
                    }
                    hash2.put(out,hash2.get(out) - 1);
                    left += len;
                }
                //更新结果
                if(count == m ){
                    ret.add(left);
                }
            }
        }
        return ret;
    }
}